As shown in Non-Patent Reference 1, the effect of surface enhanced infrared absorption (hereinafter this may be referred to as SEIRA) is actively studied these days as a phenomenon applicable to high-sensitivity and simple chemical sensors/biosensors. SEIRA sensors directly monitor the frequency of molecular oscillation, differing from dielectric sensors such as surface plasmon sensors, or resistance-detecting gas sensors, etc. Therefore, they exhibit their power in detecting the components of molecular species and in monitoring states/environments, for example, in detecting the components of biological molecules/polymers and the like and monitoring their state changes, or in monitoring the reaction process of chemical species on the surface of electrodes in fuel cells, etc. Metallic films comprising fine particles and metallic films having a rough surface morphology have a high SEIRA activity, and therefore, there are known many cases of using nano-thin films of such metallic films grown on a semiconductor/insulator substrate as sensor materials.
Heretofore, for producing SEIRA-active sensor materials, widely used is a method of forming a continuous film island-like grown on a semiconductor substrate through vacuum vapor deposition. However, the production method requires an expensive vacuum apparatus, and the sensor film produced in such a vacuum apparatus must be once taken out of the apparatus and checked one by one immediately after its production according to an infrared absorption method, and therefore the method detracts from efficient control of the SEIRA activity of the sensor materials. Accordingly, a simpler and more inexpensive production method for SEIRA sensors is desired. In addition, the SEIRA sensors produced according to the vacuum vapor deposition method are not still satisfactory in the sensitivity and the reproducibility thereof; and it is desired to realize SEIRA sensors having a higher sensitivity and more excellent in the reproducibility.
Regarding the technology relating to the SEIRA effect, Non-Patent Reference 2 discloses a report of studies relating to the kinetics and the molecular process in adsorption/desorption of fine particle film in solution using a SEIRA method; Non-Patent Reference 3 discloses a first report relating to monitoring of adsorption/desorption of metallic fine particles in solution using a SEIRA method; and Non-Patent Reference 4 discloses a report of studies relating to the molecular process in desorption of fine particle film in solution using a SEIRA method.                [Non-Patent Reference 1] M. Osawa, Bull. Chem. Soc. Jpn. 70, 2681-2880 (1997)        [Non-Patent Reference 2] D. Enders, T. Nagao, T. Nakayama, and M. Aono, Langmuir 23, 6119 (2007)        [Non-Patent Reference 3] D. Enders, T. Nagao, A. Pucci and T. Nakayama, Surf. Sci., 600, L71 (2006)        [Non-Patent Reference 4] D. Enders, T. Nagao, and T. Nakayama, Jpn. J. Appl. Phys. 46, 3020 (2007)        